A semiconductor device disclosed in Japanese Patent Application Publication No. 2017-112334 includes a semiconductor element and a heat radiator connected to a surface of the semiconductor element. The heat radiator includes a metal heat conductor connected to the surface of the semiconductor element. Moreover, the heat radiator includes a first heat conductor connected to the metal heat conductor and a second heat conductor stacked on the first heat conductor in a direction in which the semiconductor element and the heat radiator are arranged. The first heat conductor includes a plurality of first graphite layers. The plurality of first graphite layers is stacked in a first direction which is orthogonal to the direction in which the semiconductor element and the heat radiator are arranged. The second heat conductor includes a plurality of second graphite layers. The plurality of second graphite layers is stacked in the first direction which is orthogonal to the direction in which the semiconductor element and the heat radiator are arranged. Both of the plurality of first graphite layers and the plurality of second graphite layers are stacked in the first direction. In the semiconductor device in Japanese Patent Application Publication No. 2017-112334, to obtain a flexible heat conducting structure, the stacking direction of the plurality of first graphite layers and the stacking direction of the plurality of second graphite layers need to coincide with each other.
In the semiconductor device in Japanese Patent Application Publication No. 2017-112334, the semiconductor element generates heat when operating. The heat generated in the semiconductor element is radiated by the heat radiator. The heat is conducted and radiated by the metal heat conductor and the first and second heat conductors of the heat radiator. The heat generated in the semiconductor element is conducted firstly by the metal heat conductor connected to the semiconductor element, then by the first heat conductor connected to the metal heat conductor, and then by the second heat conductor stacked on the first heat conductor.
The first graphite layers have anisotropic heat conductivity. Each of the first graphite layers does not conduct much heat in the direction in which the plurality of first graphite layers is stacked. In contrast to this, each of the first graphite layers conducts heat with high heat conductivity in a direction orthogonal to the direction in which the plurality of first graphite layers is stacked. Therefore, the first heat conductor conducts heat with high heat conductivity in the direction in which the semiconductor element and the heat radiator are arranged (i.e., in the direction orthogonal to the direction in which the plurality of first graphite layers is stacked). Moreover, the first heat conductor conducts heat with high heat conductivity in a second direction (i.e., in the direction orthogonal to the direction in which the plurality of first graphite layers is stacked) which is orthogonal to the direction in which the semiconductor element and the heat radiator are arranged and orthogonal to the first direction.
Similarly, the second graphite layers have anisotropic heat conductivity. Each of the second graphite layers does not conduct much heat in the direction in which the plurality of second graphite layers is stacked. In contrast to this, each of the second graphite layers conducts heat with high heat conductivity in a direction orthogonal to the direction in which the plurality of second graphite layers is stacked. Therefore, the second heat conductor conducts heat with high heat conductivity in the direction in which the semiconductor element and the heat radiator are arranged (i.e., in the direction orthogonal to the direction in which the plurality of second graphite layers is stacked). Moreover, the second heat conductor conducts heat with high heat conductivity in the second direction (i.e., in the direction orthogonal to the direction in which the plurality of second graphite layers is stacked) which is orthogonal to the direction in which the semiconductor element and the heat radiator are arranged and orthogonal to the first direction.